Metal halide arc discharge lamps are widely used for general illumination. These lamps include an arc tube mounted within a light-transmissive lamp envelope. The lamp envelope may be evacuated or backfilled with nitrogen. The arc tube has electrodes mounted at opposite ends and contains a fill material including a starting gas, mercury and one or more metal halides. A starting electrode is typically mounted at one end of the arc tube adjacent to one of the main electrodes to assist in starting.
The arc tube can be supported within the lamp envelope using a so-called "frameless" construction as disclosed in U.S. Pat. No. 3,407,327, issued Oct. 22, 1968 to Koury et al. In the frameless construction, a strap encircles the press seal at each end of the arc tube. A lower frame member is attached between the strap at the base end of the arc tube and one of the stem leads that passes through the lamp stem. An upper frame member is attached to the strap at the dome end of the arc tube. Bulb spacers attached to the upper frame member retain the upper end of the arc tube in a fixed position relative to the lamp envelope.
The arc tube must be supported within the lamp envelope in a manner to withstand the shock to which the lamp may be subjected during shipping and handling. If the arc tube moves within the lamp envelope as a result of a shock, the arc tube may be damaged, the light output may be reduced, or electrical conductors within the lamp may be short circuited. Accordingly, metal halide arc discharge lamps are normally required to withstand shocks incurred during shipping and handling without damage. However, the shock resistant design should be easy to manufacture and should have a relatively low cost. In addition, the lamp design should be compatible with high speed, automated sealing equipment.
It is a general object of the present invention to provide improved arc discharge lamps.
It is another object of the present invention to provide metal halide arc discharge lamps wherein the arc tube is mechanically supported only from the base end of the lamp.
It is a further object of the present invention to provide metal halide arc discharge lamps wherein an upper frame member is not required.
It is still another object of the present invention to provide metal halide arc discharge lamps which are resistant to shock.
It is yet another object of the present invention to provide metal halide arc discharge lamps which are easy to manufacture and which are low in cost.